1. Field of the Invention
The present invention relates to methods and related systems for operating a downhole tool connected to coiled tubing and, more particularly, to such methods and related systems that enable the operator at the earth's surface to know the exact location of the tool within a wellbore and to determine the forces acting on such tool.
2. Description of Related Art
Knowing the location of and the magnitude and direction of forces acting on a downhole tool within a wellbore is crucial to the proper operation of tools and devices that must interact with in-place wellbore equipment. For example, those skilled in the art know that an operator at the earth's surface must be able to know the location of the lower end of a kickover tool in relation to an existing side pocket mandrel, as well as direction of the forces applied thereto when the kickover tool is introduced into the wellbore. If the kickover tool is operated in an incorrect location or excessive force is applied to it within the wellbore, damage to the tool and/or the wellbore may result. More importantly, the recovery of valuable wellbore hydrocarbons may be abated if the tool and/or the wellbore is damaged.
Continuing the above example, when a kickover tool is run by gravity on a wireline the operator generally knows the location of the kickover tool within the wellbore by reading an indicator of the footage of wireline that has been introduced into the wellbore, and/or by watching a weight indicator for an increase or a decrease in wireline tension to determine if the tool has been properly located or set within the wellbore. The kickover tool has a finger adapted to engage a detent within the side pocket mandrel, and is activated by a predetermined strain force or an impact force. Standard procedure with this type of wireline operation is to unroll sufficient wireline so that the kickover tool is lowered past the detent within the side pocket mandrel. Then, the wireline is slowly retrieved while a wireline load indicator is closely monitored at the earth's surface. When the kickover tool's finger has become engaged in the detent, the load applied to the wireline will sharply increase, which will give the operator a positive indication that the kickover tool is properly oriented and landed within the side pocket mandrel. Thereafter, the operator can utilize wireline jars to repeatedly apply controlled impact forces to the kickover tool to activate it and, for example, set a gas lift valve within the side pocket mandrel. A similar procedure can be used to set wireline locks, sliding sleeves, operate running, pulling and fishing tools, or numerous other wireline operations which require precise location and application of impact forces.
In wellbores where such wireline operations cannot be used, such as in deviated or horizontal wellbores, coiled tubing is now being used because of its relative rigidity which allows it to be pushed further into the wellbore, and especially into horizontal sections of the wellbore. However, due to the rigidity of coiled tubing, the operator may not know the exact location of the end of the coiled tubing and the precise location of the tool within the wellbore, nor the forces generated at the lower end of the coiled tubing. While coiled tubing is more rigid than wireline, it is inherently ductile and because of this coiled tubing will tend to snake or form long helical loops within the wellbore when a downward force (ie. a compressive load) is applied thereto. The result is that the operator will know how many feet of coiled tubing has been introduced into the wellbore, yet the operator will not know the exact location of the end of the coiled tubing. Sometimes the best location estimate of even skilled coiled tubing operators is several hundred feet in error. This helical looping also masks the forces generated at the lower end of the coiled tubing so that the operator can easily overstress a downhole device.
There is a need for a method and a related system for determining at the earth's surface the exact location of the end of coiled tubing within the wellbore and the magnitude and the direction of forces acting thereupon, and which can be used in vertical wellbores, as well as deviated and horizontal wellbores.